In oceanographic research it is frequently necessary to obtain samples of water from a series of discrete depths in the ocean. For certain other purposes it is desirable to obtain a series of water samples at discrete time intervals from a fixed location. Where relatively gross characteristics of the water are to be measured or analyzed, such as salinity or dissolved oxygen, a relatively small sample volume has been adequate, and a variety of simple and efficient sampling apparatus have been available for such purposes.
However, where relatively more dilute substances are being sampled for analysis or study, such as dissolved organic matter, trace elements, suspended particles, or chemical pollutants, an inconveniently large volume of water needs to be collected before an adequate sample can be filtered out or otherwise extracted.
Apparatus has been developed in the past for obtaining large volume water samples for shipboard extraction, but the methods used have been tedious or even dangerous in rough weather. As an alternative to large volume water filled bottles or bags, various pumping methods have been devised in the past for bringing aboard relatively large water samples. Generally, such methods have consisted of shipboard pump and extraction systems and a intake tube extending down to the desired sampling depth. Where a single large volume sample of water is needed from near the surface, and where sampling tube contamination from previous sampling is unimportant, a simple pumping system has been satisfactory. However, where a series of samples are needed, either at various depths or spaced at intervals over a period of time, and where contamination must be avoided, the shipboard pump with single intake tube and extraction system is not suitable.